1. Field of the Invention
The present invention generally relates to a disk device and a method of compensating a disturbance in the disk device and, more particularly, to a disk device positioning a head by a rotary actuator and a method of compensating a disturbance in the disk device.
In a magnetic disk device, a rotary actuator is generally used as a mechanism to move and position a head. The rotary actuator is greatly affected by a rotative disturbance due to a structure thereof.
Thus, there is proposed a measure for compensating an influence of such a disturbance to a positioning of a head. The measure comprises mounting an acceleration sensor on a body or a circuit board of a magnetic disk device, sensing an external vibration and a vibration caused by a seek reaction-force of the magnetic disk device itself, and controlling a disturbance compensation by using information detected so as to prevent the vibrations from affecting a positioning of a head.
2. Description of the Related Art
First, a description will be given of a structure of a magnetic disk device.
FIG. 1 is an illustration of a structure of a conventional magnetic disk device. FIG. 2 is a block diagram of the conventional magnetic disk device.
A magnetic disk device 100 comprises a disk enclosure 110 and a printed circuit board 120. The disk enclosure 110 incorporates a magnetic disk 111, a spindle motor 112, a magnetic head 113, an arm 114, and a voice coil motor (VCM) 115. The spindle motor 112 is driven by a driving signal from the printed circuit board 120 so as to rotate the magnetic disk 111 at a constant speed in directions indicated by an arrow A. The voice coil motor 115 is driven by a driving signal from the printed circuit board 120 so as to oscillate the arm 114 in directions indicated by an arrow B. The magnetic head 113 is moved in a radial direction together with the arm 114 being oscillated in the directions indicated by the arrow B.
A signal read by the magnetic head 113 is supplied to a head IC 116. The head IC 116 amplifies the signal from the magnetic head 113. The head IC 116 also amplifies a signal to be recorded on the magnetic disk 111, and supplies the amplified signal to the magnetic head 113.
The signal supplied from the magnetic head 113 and amplified by the head IC 116 is supplied to the printed circuit board 120. The printed circuit board 120 comprises a hard disk controller (HDC) 121, a RAM 122, a ROM 123, an MPU 124, a read channel (RDC) 125, a servo controller (SVC) 126, and linear acceleration sensors 127 and 128.
The information (signal) read by the magnetic head 113 and amplified by the head IC 116 is decoded by the read channel 125 and the hard disk controller (HDC) 121, and then is supplied to a higher system 130.
On the other hand, information from the higher system 130 is supplied to the hard disk controller (HDC) 121 and the read channel 125, and is decoded thereby. The decoded information is supplied to the head IC 116, and is amplified thereby. The amplified signal is supplied to the magnetic head 113, and is recorded on the magnetic disk 111.
Next, a description will be given of the printed circuit board compensating a rotative disturbance of the conventional magnetic disk device.
FIG. 3 is a plan view of the conventional printed circuit board as an example. The conventional magnetic disk device 100 has the two acceleration sensors 127 and 128 mounted on the printed circuit board 120, and conducts a disturbance compensation by calculating an angular acceleration α from outputs G1 and G2 of the two acceleration sensors 127 and 128 and a mounting distance L between the two acceleration sensors 127 and 128, using the following expression (1).α=(G1−G2)×9.8/L[rad/s2]  (1)
FIG. 4 is a block diagram of a main part of a magnetic disk device conducting a rotative-disturbance compensation by using outputs of the conventional acceleration sensors.
An output Gn of the acceleration sensor 127 or 128 is filtered through a filter unit 131, and undergoes a gain adjustment in a gain-adjusting unit 132, and then is supplied to a subtracter 133 as a compensation signal Sb. The subtracter 133 is supplied with a control amount signal Sa from a controller 134. A subtracter 135 is supplied with information of an aimed position and information of a positioning error of a controlled object 136 so as to supply differential information therebetween to the controller 134. The controller 134 generates the control amount signal Sa (a tracking error signal) based on the differential information supplied from the subtracter 135. The control amount signal Sa is supplied to the subtracter 133, as mentioned above, in which the compensation signal Sb is subtracted from the control amount signal Sa, giving a driving information S. The driving information S is supplied to a VCM (voice coil motor) that is the controlled object 136.
As described above, the conventional magnetic disk device conducting a disturbance compensation has the acceleration sensor in order to sense disturbing vibrations. Consequently, the conventional magnetic disk device has a complicated structure, and thus becomes costly. Moreover, since an acceleration sensor generally senses only a linear acceleration, the conventional magnetic disk device has to have a plurality of the acceleration sensors 127 and 128 in order to sense a rotational acceleration. This raises the cost of the conventional magnetic disk device much higher.